1. Field of the Invention
This invention relates to an arrangement for relieving stress on the connection between electrical conductors and an electric element that is contained in a generally flat, bendable, elastic carrier when manufacturing seats, as well as a method for assembling the arrangement.
2. Background Art
Seats often contain one or more electric elements or circuits that are used, for example, to heat the seat or to sense whether someone is sitting in the seat. Such electric elements are particularly common in vehicle seats. These elements or circuits must be connected to an external electrical system such as a vehicle's power supply or display circuitry: First, power supply leads must be connected to the elements; and second, where the elements include sensors, the output signals from the sensors must be led from the seat to other circuitry elsewhere in the vehicle.
The elements or circuits in seats are typically mounted on or embedded in a generally flat, sheet-like carrier or base that is installed in the seat. One of the functions of the carrier is to locate, fix and isolate each element its entire extent so that it does not short circuit itself or come into contact with other electrically conducting materials. The carrier must also shield and protect the element, in part so that the person sitting in the vehicle seat does not feel it and in part so that the load on the seat is not enough to break it altogether. The carrier must therefore be bendable, elastic, and rugged enough to withstand the stresses that arise.
Electrically heated vehicle seats, for example, normally have one or more loops of heating wire that are supplied with electrical energy via a thermostat or an adjustable control. The carrier in known seat-heating assemblies is typically formed of two layers of fabric that surround the heating wire. One of these fabric layers may be coated with a foam material such as polyester foam. The heating wires in such a known seat-heating assembly are usually connected to a contact device that makes it possible to connect the assembly easily to the electrical system of the vehicle when the seat is mounted in the vehicle. The contact device also makes it possible to break the connection with the vehicle's electrical system if the seat has to be removed from the vehicle.
It has been found possible to at least partially automate the manufacture of seat-heating assemblies in order to lower the manufacturing costs. Using known assembly methods, several heating loops are laid out on a web of material. A second material web is then joined with the first material web by gluing and pressing. The joined web is then stamped into suitably shaped pieces, which form complete assemblies after electrical contact devices are mounted on them.
Because this manufacturing process includes pressing and stamping, it has been necessary to mount the contact devices as the last step in the manufacturing chain. Mounting the contact devices has hitherto been done in such a way that the two material layers of the carrier are manually pulled apart enough to expose the ends of the resistive wires, after which the conductors of the contact device are connected to these exposed ends by twisting or soldering. This final work step is both time-consuming and work-intensive and this in turn has meant that the manufacturing cost of each seat-heating assembly has been relatively high. Efforts to provide for a secure assembly in a less costly manner have also been hindered by the stringent requirements for the ability of the assembly to resist tensile stresses: the electrical conductors must normally be able to withstand tensile forces of approximately 250-300 N. Similar production methods are used, and similar problems arise, when the seat assembly includes other types of electrical elements in the seats.
What is needed is therefore an arrangement for relieving mechanical stress when connecting the electrical conductors in a seat-heating assembly and a method for assembling the arrangement that makes it possible to completely automate the manufacturing procedure.